1. Field of the Invention
The present invention relates to a humidifier for humidifying reactant gases for a polymer electrolyte fuel cell system, and more particularly, to a humidifier for humidifying reactant gases which is needed for the development and actual operation of a polymer electrolyte fuel cell system and is capable of adjusting an amount of water while reducing electrical power consumption and its size, thereby maintaining an optimal temperature and humidity of the reactant gases supplied to a polymer electrolyte fuel cell.
2. Description of the Prior Art
In general, a fuel cell system, which is widely known as an electrical power generation system, generates electrical power by electrochemical reactions. Such fuel cell systems have very extensive ranges of applications from small to large-sized systems for reasons that they work with higher energy efficiency and also produce no pollutants in contrast to the conventional combustion engines. The fuel cell systems are classified according to the kind of an electrolyte that is used namely, alkaline type, phosphoric acid type, molten carbonate type, solid oxide type, polymer electrolyte type, etc.
Among the above-mentioned various types of fuel cells, the polymer electrolyte fuel cell system is particularly suitable for an automobile or a mobile electric power source because it has advantages in that it is operable even at a relatively low temperature, its electrolyte is solid so that there is no danger of leakage of the electrolyte, and its maintenance and repair are convenient.
In a polymer electrolyte fuel cell system, the polymer membrane, used as a polymer electrolyte, through which the protons (H+) move, must be in a sufficiently moistened condition to provide an adequate ionic conductivity. In the case when the electrolyte membrane is dehydrated, the fuel cell system is not normally operable due to the degradation of its ionic conductivity. For this reason, the humidifying process is an indispensable part of the fuel cell system which prevents the electrolyte from drying.
The characteristics of the polymer electrolyte fuel cell system are greatly influenced by manufacturing and operating techniques. Accordingly, the operating parameters such as temperature of a fuel cell, flow rate, pressure, and temperature of reactant gases, and humidity should be adjusted to be in an optimal condition by means of a humidification apparatus.
As illustrated in FIG. 1, the gas supply apparatus comprises: an inlet pipe 1 through which the reactant gases are supplied from a reactant gas reservoir; a flux regulator 2 for adjusting the flow rate of supplied reactant gases; a humidifier 3 for humidifying the reactant gases; a gas supply pipe 4 for supplying the humidified reactant gases to the fuel cell 5; a pressure regulator 7 for adjusting the pressure of reactant gases inside the fuel cell 5; an outlet pipe 6 through which the reactant gases are emitted from the fuel cell 5 by the operation of the pressure regulator 7; a fuel cell thermocouple 8 which is installed inside the fuel cell 5 and is used in a temperature monitor 10 for controlling a coolant regulator 9; and a coolant regulator 9 for cooling the fuel cell 5.
The conventional humidifier that is commonly positioned between the gas supply apparatus and the fuel cell 5, is shown in FIG. 2. The humidifier, which humidifies reactant gases by passing through heated water comprises: a humidifier thermocouple 13 installed in the middle of a humidification vessel 17; a heater 14 disposed along the circumferential surface of the humidification vessel 17; insulating material 15 surrounding the outer surface of the heater 14; a water level gauge 16, which is installed at one side of the humidification vessel 17 and which indicates the water level of the humidification vessel 17; a gas supplying pipe 4 through which the humidified reactant gases are supplied to the fuel cell 5; and an inlet pipe 12 through which the reactant gases is supplied to the humidifier.
However, the above-described conventional humidifier is defective in that it is difficult to adjust the size of bubbles generated inside the humidifier and the amount of water needed for humidification, heating water consumes excessive electrical power, and moreover, the overall size of the humidifier increases according to an increase in the capacity of a fuel cell system.
In consideration of a mobile power supply requiring a restricted size and electrical power consumption by supplemental devices being minimized, the conventional humidifier has several limitations to being used in actual applications, since additional electrical power for heating water and an increase in overall size is required.
In another conventional method of humidifying reactant gases using a membrane, there is a drawback in that additional humidification devices should be mounted inside a fuel cell. As a result, the inner construction of a fuel cell is not only complicated but the size of a fuel cell is increased. Moreover, such apparatus has another drawback that the humidification conditions are varied with the state of a membrane, temperature and pressure of a fuel cell.